In recent years, a display device which displays an image on a display panel using a backlight has been widely used in various fields of industry. For example, a projector (PJ) or an FPD (Flat Panel Display) which displays a video signal supplied from the outside of a device on a display panel using a liquid crystal or a micromirror device has been widely used. Such a display device includes the display panel using the liquid crystal or the micromirror device, and an optical member of a backlight (light source; BL: backlight) which irradiates the display panel with light, such as a super high pressure mercury lamp, a W/RGB LED (Light Emitting Diode) or a cold cathode fluorescent lamp (CCFL). Further, the display device includes, as circuit units, a BL driving unit which controls luminance of light emitted by the backlight, and a circuit which drives the display panel (see Patent Document 1).
When the above-described display device is used as a display device for a graphic design or a medical purpose, display characteristics (stability of color display) designated in advance are required to be maintained for a long period of time.
However, there is a problem associated with the display device in that luminance of a displayed image is degraded and chromaticity gradually yellows over time when the display device is used for a long period of time.
This yellowing of the chromaticity occurs as color balance of each of color components of R (Red), G (Green) and B (Blue) is changed since deterioration speed of luminance deterioration is different according to light emitting materials of each color component of R, G and B when luminance of the RGB light emitting material in the backlight deteriorates over time.
Detection of luminance of light emitted by the backlight using a built-in optical sensor, monitoring of a light emission state of the backlight, and control of the luminance of the backlight are generally performed as a solution to the luminance deterioration of the backlight.
Further, as another solution to the degradation of the luminance of the backlight, for example, in a liquid crystal display device illustrated in FIG. 5, a luminance value in an initial state of a backlight 102 driven by a BL driving circuit 101 is measured and stored in an initial luminance storage unit 104 in advance, and a chromaticity calculation unit 105 calculates current chromaticity based on a difference between the luminance value of this initial state and a current luminance value of the backlight 102 detected by a BL luminance detection unit 103.
Also, a chromaticity correction value calculation unit 107 obtains a difference between white point chromaticity calculated by the chromaticity calculation unit 105 and target white point chromaticity stored in a target white point chromaticity setting unit 106, and calculates this difference as a chromaticity correction value.
Then, a chromaticity correction circuit 108 corrects chromaticity of a video signal input from the outside using the chromaticity correction value calculated by the chromaticity correction value calculation unit 107, and outputs the resultant video signal to a display unit 100 including a display panel configured of a liquid crystal or the like.
However, detection of the white point chromaticity performed by the chromaticity calculation unit 105 requires detection of a luminance value (backlight luminance value) of the light emitted by the backlight when a BL (Back Light) driving level (backlight driving level) and a temperature of the backlight (backlight temperature) in a reference state when the luminance value of the initial state is measured are set.
There are the following problems associated with performance of the correction of the chromaticity due to performance of the detection of the backlight luminance value at this temperature of the reference state.
(a) In a period of use by a user, since a backlight driving level is arbitrary, the backlight driving level used in performing the correction of the chromaticity is not the same as the backlight driving level in the reference state. Therefore, the backlight luminance value corresponding to the reference state cannot be detected, and white point chromaticity for obtaining the chromaticity correction value used for correction of the chromaticity cannot be accurately estimated.
(b) It is necessary for the user to regularly stop use of the liquid crystal display device and execute a process of obtaining the above-described chromaticity correction value, which is a burden to the user.
(c) It is difficult to measure the backlight luminance value at a backlight temperature at which the backlight luminance value of the reference state has been measured, and it is not possible to calculate an accurate chromaticity correction value and perform highly precise correction of the chromaticity.